Energy Efficiency Basics

Energy-efficient windows can help reduce your utility bills and make your home more comfortable. Not to mention the peace of mind that comes with knowing you’re helping the planet by minimizing environmental impact. Marvin offers a variety of window and door options that help you achieve long-term performance and energy cost savings, in any climate.

QI need new windows. What’s the first thing I need to know when it comes to windows and energy efficiency?

AReplacing windows with energy-efficient ones can help reduce your utility bills, but the benefits go much further. Choosing energy-efficient windows makes your home more comfortable, as their performance determines how much heat comes in and escapes out through the windows.

QHow do I know if a window or a door is energy efficient?

ACertification programs such as those administered by the National Fenestration Rating Council (NFRC) and ENERGY STAR provide ratings designed to indicate a window or door's efficiency. Various performance ratings — like U-factor and Solar Heat Gain Coefficient — measure a product’s effectiveness in insulating and blocking heat from the sun, among other things. See the Glossary of Terms.

U-Factor:Simply put, U-factor measures how well a window keeps heat inside your home. It’s a measure of total heat flow through a window or door from room air to outside air. Lower numbers indicate greater insulating capabilities. It’s a particularly important measure for climates with colder winters.

Solar Heat Gain:If U-factor denotes how much heat leaves your home, the Solar Heat Gain Coefficient (SHGC) measures how much radiant heat enters your home. All you really need to remember is: The lower the number, the less heat a window lets in.

Visible Transmittance (VT):The amount of visible light transferred through a window. Low E coatings can reject solar heat gain without reducing visible light to pass through the glass. A high VT is desirable to maximize daylight.

NFRC example

QAre tax credits still available for energy-saving window and door replacement?

A Under the Bipartisan Budget Act of 2018, which was signed in February 2018, a number of tax credits for residential energy efficiency that had expired at the end of 2016 were renewed and extended through December 31, 2017. To qualify, windows must meet ENERGY STAR requirements and be installed at the taxpayer’s primary residence. The tax credit equals 10% of product cost, excluding installation costs, up to $200 for windows and up to $500 for doors. Homeowners are limited to $500 total energy efficient tax credits, including claims from previous years. See and click how to apply for details.


QWhat does it mean to be an ENERGY STAR-certified window or door?

ATo obtain ENERGY STAR certification, a window or door must meet a set of requirements that are determined by the U.S. government. Those requirements differ based on geography, meaning a window that’s being installed in Minnesota has different requirements than one in Florida. The certification is meant to indicate that the window is energy-efficient in the region where it will be used, and can help homeowners save on energy costs.

Energy Star Zone Map

QI heard there were changes to ENERGY STAR guidelines. Do those affect me and my home?

AIn January 2016, ENERGY STAR updated requirements for windows in what they define as the “Northern Region,” after updating requirements for other parts of the country in 2015. Those changes raised the bar for ENERGY STAR certification, but just because ENERGY STAR tightened their requirements does not mean windows released prior to the updated guidelines are any less efficient.

Energy Star Criteria

QDoes my window need to be ENERGY STAR certified in order to be energy efficient?

ANo. While an ENERGY STAR label can be helpful in identifying energy-efficient windows, every home is unique. ENERGY STAR provides a one-size-fits-all guideline but does not take into consideration, for example, the orientation of the house or the number or size of windows and associated Solar Heat Gain. A window expert like your Marvin dealer can help determine which products will work best for you.

ENERGY STAR also recognizes products that meet high energy-efficiency guidelines. Marvin offers the industry’s widest selection of wood and clad wood products that meet these rigorous criteria. Link to Most Efficient product list.

Energy Star Criteria

Glass and Glazing

Glass and Glazing

QCan you help me to better understand the numbers? What’s a good U-factor number? What’s a good SHGC?

ADifferent homeowners seek out different levels of efficiency, but a “good” U-factor is <.30. A “good” Solar Heat Gain rating, meanwhile, on a scale from 0 to 1, is relative to climates in different regions. Low SHGC numbers are best for southern climates where there’s intense sun exposure, whereas higher SHGC values make the most sense for regions with cold winters.

QCan you explain Low E coatings?

AThe ability of a material to radiate energy (heat) is called its emissivity. Extremely thin coatings of special low emissivity (Low E) metallic material are applied to glass panes used in windows and doors to boost their energy efficiency. Low E coatings, usually applied to the inside layers of insulating glass, manage the amount of light and heat either conducted through a window or reflected away from it.

INSULATING GLASS (IG):Two or more glass panes separate by an air space to reduce thermal transfer.

LOW E:Low E stands for low emissivity. Microscopically thin, transparent metal or metallic oxide layers deposited on a glass surface suppress radiative heat flow and reflect interior infrared energy (heat) back to the inside, reducing heat loss through the glass. Various Low E coating options can manipulate heat gain to match different climate needs.

GAS FILLS:Argon or krypton mixes slow the movement of warm and cool air in IG airspaces and improve thermal performance.

Thermal Glass

QAre triple pane windows the best? The more panes the better, right?

ANot always. Triple-pane windows work best when enhanced energy performance is a key objective. Tripane offers a range of low-E configurations for greater Solar Heat Gain control, including panes filled with argon or krypton-argon gas for added efficiency. But no matter how many panes there are, if the window is poorly constructed, poorly installed or allows air leakage, it will not be efficient.

Tripane Corner
Glazing Options

Energy efficiency is achieved through the use of various window technologies. Low E coatings, frame materials, glazing types, spacers, gas fill, and weatherstripping all contribute to efficient windows.

Energy ratings for windows and doors are certified by the National Fenestration Rating Council (NFRC). See NFRC ratings for any Marvin product on the Energy Information Finder Tool page, or by opening the Professional Resources tab on any product page.

High Performance

High Performance

QWhat else do I need to know if I want to make my home super energy efficient?

AIt’s easier than ever before. Modern sustainable building methods, like Passive building, LEED® (Leadership in Energy and Environmental Design) and Net Zero building can help you minimize environmental impact and maximize energy efficiency. ENERGY STAR also offers a “Most Efficient” list, a distinction that recognizes products that deliver superior efficiency through cutting-edge technologies and innovations. Marvin is an industry leader in offering a wide selection of products that meet these rigorous criteria.

Learn more about Most Efficient products at the EPA ENERGY STAR website.

QIs sustainable building the same as high performance building?

ASustainable building refers to both a structure and to processes that are environmentally responsible and resource-efficient throughout a building's life-cycle: from siting to design, construction, operation, maintenance, renovation, and demolition.

According to the National Institute of Building Sciences, high performance building integrates and optimizes all major high-performing building attributes, including energy efficiency, durability, life-cycle performance, and occupant productivity.

QCan I make my home a high performance building?

AThere are methods to optimize energy efficiency in a home environment, most easily with new construction. One way is to plan for a building to generate at least as much energy as it consumes. Net Zero homes and Zero Net Ready homes are carefully designed structures that currently or in the future make use of alternative energy solutions such as wind, solar and/or geothermal systems.

Passive building is another high performance construction concept. It achieves significant energy savings by creating a superinsulated building envelope that minimizes heat loss and prevents air leakage. Because the house is airtight, ventilation with high efficiency heat exchange continuously filters fresh air. Passive House Certification is available to help structures meet Passive House Institute U.S. building standards.

Certified Windows

You don’t need to build a Net Zero or Passive home to dramatically improve energy performance in your home. Whether replacing windows in an existing home or designing a new construction, there are plenty of energy-saving windows to choose from.

Marvin has more than 14,000 certified window and door product/glass options that meet a .20 or lower U-factor for high performance. Talk to your Marvin representative for help selecting windows and doors that best meet your energy efficiency goals.

Net Zero White Paper


Net Zero White Paper